The 52-47 vote fell short of the 60 votes needed to cut off debate under Senate rules. It was a sound defeat for Democrats who say the U.S. military campaign, in its fifth year and requiring 158,000 troops, cannot tame the sectarian violence in Iraq.

Hawai'i's Democratic U.S. Sens. Daniel Akaka and Daniel K. Inouye both voted for the legislation.

"We have to get us out of a middle of a civil war" said Sen. Joseph Biden, D-Del., who chairs the Foreign Relations Committee. A political solution must be found "so when we leave Iraq, we don't just send our children home, we don't have to send our grandchildren back."

As members cast their votes, Secretary of State Condoleezza Rice hurried between private meetings with lawmakers in their Capitol Hill offices to make the administration's case for the war.

On a trip to Afghanistan, chairman of the Joint Chiefs of Staff Gen. Peter Pace said the U.S. "can do whatever it is we want to do to have a dialogue about how to fight this enemy. But the bottom line is that as long as our enemy is sworn to destroy our way of life, we are going to be in a war."

The Democratic proposal, by Sens. Carl Levin, D-Mich., and Jack Reed, D-R.I., would have required President Bush to start bringing home troops within 120 days and complete the pullout by April 30, 2008. Under the bill, an unspecified number of troops could remain behind to conduct a narrow set of missions: counterterrorism, protecting U.S. assets and training Iraqi security forces.

Republicans were mostly unified in their opposition to sidetrack the legislation, with four exceptions. Three Republicans — Sens. Gordon Smith of Oregon, Olympia Snowe of Maine and Chuck Hagel of Nebraska — announced previously they support setting a deadline on the war.

Sen. Susan Collins, R-Maine, who is up for re-election next year, also voted to advance the bill. Spokesman Kevin Kelley said Collins believes the measure should be subject to a simple majority vote and not the 60 votes needed to end a filibuster. She opposes the legislation, however, Kelley said.

Other GOP members, while uneasy about the war, said they could not support legislation that would force Bush to adhere to a firm pullout date.

"The amendment tells our enemies when they can take over in Iraq," said Sen. Saxby Chambliss, R-Ga., who also is up for re-election next year.

The bill "is the wrong approach at the wrong time," he added.

Senate Majority Leader Harry Reid, D-Nev., a strong supporter of troop withdrawals, nonetheless cast the sole Democratic vote to block the legislation — a parlimentary tack that allows him to resurrect the measure at a later date.

The maneuvering occurred as the Senate debated a broad defense bill that includes a pay raise for the troops, revised regulations for detaining suspects in the war on terror and an increase in the size of the Army and Marines. Following the vote, Reid said he would suspend work on the measure, to which the Democrats sought to attach the troop withdrawal provision, until a date to be determined.

By pulling the defense bill, Reid ensured the Iraq debate would remain focused on legislation ordering troop withdrawals and not move on to consideration of softer proposals backed by several Republicans. It paved way for another contentious debate on the war this September, when Iraq commander Gen. David Petraeus delivers his assessment of the recent troop buildup.

Democrats are hoping that, by then, enough GOP members will turn against Bush on the war and vote to bring troops home.

Among lawmakers scheduled to meet with Rice were Biden, Smith, Sen. John Warner, R-Va., and House Republican leader John Boehner of Ohio.

The vote came after a rare, round-the-clock session Democrats used to highlight Republican support for Bush's Iraq strategy. Republicans said the all-nighter was a useless political stunt.

"All we have achieved are remarkably similar newspaper accounts of our inflated sense of the drama of this display and our own temporary physical fatigue," said Sen. John McCain of Arizona, presidential candidate and the top Republican on the Armed Services Committe.

Most senators got a chance for a few hours of shuteye even while a handful of their colleagues took turns droning on through the night with floor speeches.

With a half-dozen spectators watching from the gallery, Republicans Collins and Sen. John Thune of South Dakota were among those speaking during the long night, joined by Democrats Bob Menendez of New Jersey, Debbie Stabenow of Michigan and Jim Webb of Virginia. McCain finished his speech around 4:10 a.m. He was followed by White House hopeful Hillary Clinton, D-N.Y.

While the issue was momentous — a war more than four years in duration, costing more than 3,600 U.S. troops their lives — the proceedings were thick with politics.